Physicochemical insights into semiconductor properties of a semitransparent tantalum nitride photoanode for solar water splitting

The self-conductivity of tantalum nitride (Ta3N5) thin film-based semitransparent photoanodes was found to promote the current originating from the photoelectrochemical oxygen evolution reaction (PEC OER) without a conducting substrate. With surface modification by the NiFeOx-electrocatalyst, an optimized Ta3N5 thin film fabricated directly on a transparent insulating quartz substrate generated a photocurrent density of & SIM;5.9 & PLUSMN; 0.1 mA cm(-2) at 1.23 V vs. the reversible hydrogen electrode under simulated AM 1.5G solar illumination. The correlation between the PEC OER performance of NiFeOx-modified Ta3N5 photoanodes and the electrical properties of Ta3N5 thin films was investigated based on the Hall effect measurements. By changing the nitridation conditions, these properties can be tuned so that the higher the Hall mobility (0.2 to 1.7 cm(2) V-1 s(-1)) and the lower the carrier concentration (10(20) to 10(19) cm(-3)). The surface chemical states of Ta3N5 thin films were investigated using X-ray photoelectron spectroscopy as a means of evaluating surface oxygen impurities and nitrogen vacancies, which may correlate with the PEC OER performance and the electrical properties of the material.

Automated summary

The self-conductivity of tantalum nitride (Ta3N5) thin film-based semitransparent photoanodes can enhance the current in the photoelectrochemical oxygen evolution reaction (PEC OER) without a conducting substrate. By modifying the surface with NiFeOx-electrocatalyst, an optimized Ta3N5 thin film directly fabricated on a transparent insulating quartz substrate achieved a photocurrent density of about 5.9 ± 0.1 mA cm-2 at 1.23 V vs. the reversible hydrogen electrode under simulated AM 1.5G solar illumination. The relationship between the PEC OER performance of NiFeOx-modified Ta3N5 photoanodes and the electrical properties of Ta3N5 thin films was investigated using Hall effect measurements.